Preheat the oven to 350 degrees F. Cook the pasta shells according to the package directions. Drain and set aside.
In a large skillet brown the ground beef while breaking it up into chunks with a spatula. Drain any excess grease. Add the taco seasoning and the water and cook, stirring occasionally until there is no water left.
Combine the cooked taco meat with the pasta shells, salsa and 1 cup of shredded cheese. Mix well.
Pour the mixture into a lightly greased 9×13 inch baking dish. Top with the remaining cheese and crushed Doritos.
Place into the oven and bake for 20-30 minutes or until the cheese has melted and the casserole is bubbly.